Interpretive Summary: Infection by the single-celled parasite, Toxoplasma gondii, is common in man and animals. Humans become infected by eating undercooked infected meat or ingesting the resistant stage of Toxoplasma (oocysts) in the environment. Infections in free range-range chickens is indicative of Toxoplasma infection in the environment because chickens feed from the ground. Scientists at the Beltsville Agricultural Research Center and Centers for Disease Control, Atlanta, Georgia, report isolation and moleular characterization of Toxoplasma gondii strains from free-range chickens from Argentina. Thee results will be of interest to public health workers, parasitologists and veterinarians.

Technical Abstract:
The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 61 free-range chickens (Gallus domesticus) from provinces of Santiago del Estero and Entre Rios, Argentina was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT), and found in 25 chickens with titers of 1:5 in 6, 1:10 in 1, 1:20 in 2, 1: 40 in 1, 1: 80 in 2, 1: 60 in 4, 1:120 in 2, 1: 640 in 3, and 1:1,280 or more in 4. Hearts, pectoral muscles, and brains of 22 seropositive (MAT 1:10 or higher) chickens were bioassayed individually in mice. Tissue from 39 chickens with titers of 1:5 or less were pooled and fed to 3, T. gondii-free cats. Feces of cats were examined for oocysts, but none was found. Toxoplasma gondii was isolated from 17 of 22 chickens with MAT titers of 1:10 or higher. Genotyping of these 17 isolates using polymorphisms at the SAG2 locus indicated that 4 were Type I, 3 were Type II, and 10 were Type III. Toxoplasma gondii isolates (2 Type I and 1 Type III) from 3 chickens were virulent for mice and 1 Type I was not mouse virulent. Prevalence of T. gondii antibodies in chickens varied among regions being 3 times greater in the humid Pampeana region (61.2%) than in the semi-arid plain of Santiago del Estero (20%).